— Rolling with inevitable changes is one thing. Changing schemes every season is another.

The latter has been the reality for Philadelphia Eagles safety Nate Allen, who had to take a few steps backward in his career before moving forward to where he is now, as one the starting safeties a year after his spot on the 53-man roster was thought to be in jeopardy.

Allen returns to play for his fourth NFL defensive coordinator and fourth scheme this season. But unlike the unstable situation he entered as a second-round draft pick in 2010, everyone gets the sense this system will be in place for a while.

Allen couldn't be happier, and he's proved it by the way he's played throughout training camp and the preseason, ending what was supposed to be a competition many thought Earl Wolff would win for a starting spot along veteran newcomer Malcolm Jenkins. The Eagles require their safeties to be interchangeable, so there is no real difference between the spots, although Allen plays the deep middle (free safety) more.

Now he just seems more ready than ever to break out, defensive coordinator Bill Davis hinted on Sunday.

"I would put Nate in the same category as [LB] Mychal Kendricks and some of the other guys," Davis said. "Now that we are in Year 2 in a scheme and the words haven't changed on them, we did not change the scheme on them, the structure's in place, I think they're big concept learners. With some people when you learn the concept and understand the concept, now the details become easier."

"I think we've seen Nate grow because his understanding is now letting him calm his mind to slow down and he's seeing more because he understands his landmarks. He understands where his eyes need to be placed. He understands the two-gap system of not having a safety be a primary run defender. All those things are growing and you see Nate play better and better."

Davis also claimed that Allen's starting spot wasn't secured yet, perhaps missing what head coach Chip Kelly said the day before about the plan for starters to be held out of Thursday's preseason finale against the New York Jets and not realizing it was OK to admit it.

"I see Earl Wolf playing, definitely," Kelly said. "I don't think Nate will play, but that depends on the depth at that position. … It means [Wolff] needs a lot more reps."

At any rate, the job is Allen's, just as it was last year coming out of camp, and he went on to start every game for the first time in a career that couldn't seem brighter after an almost endless series of setbacks, which began with him wrecking his knee (rupturing a patella tendon) near the end of his rookie season.

Allen was back in time to start the next season under a new safety-unfriendly system forced upon new defensive coordinator Juan Castillo, who in a bizarre series of moves was promoted to that position from offensive line coach after head coach Andy Reid fired Sean McDermott following a 21-16 playoff loss to offensive juggernaut and eventual Super Bowl champion Green Bay.

But he was not fully recovered.

On top of that, by the middle of the following season, the entire back end of the defense was confused by the Wide 9, an alignment defensive line coach Jim Washburn brought with him from the Tennessee Titans that completely sells out to the pass, putting enormous pressure on all defensive backs to provide run support.

Castillo and Washburn didn't survive the season, and Todd Bowles was promoted to coordinator in an attempt to pick up the pieces. Despite scrapping the Wide 9, Bowles saw the defense grow infinitely worse under him than it had become under Castillo.

All of this led to a mass coaching purge and yet another new system for Allen, whose play had steadily declined until Kelly and Davis arrived, restoring order and creating an environment where Allen felt he could flourish again.

It's why he chose to re-sign with the Eagles this year after becoming a free agent.

"I have a year under my belt with it," Allen said. "But I'm still learning it and perfecting things, but I definitely feel comfortable in everything and I just want to keep fine-tuning everything and get ready for the regular season."

After intercepting five passes over his first two seasons, Allen had none in 2012 and one last season, but compiled a career-best 94 tackles.

He knows he can get more turnovers this season if he plays the scheme the way he knows how.

"For any safety I'd imagine it makes your job a lot easier," Allen said. "You're not designated to a certain gap on certain plays and you're freed up and you can roam more and be kind of a free player at certain times, and this just makes you real aggressive on the back."

After four years, 60 games and 55 starts, Nate Allen appears ready to deliver his best play.